Plastics are becoming increasingly used by the manufacturing industry. Plastics often provide benefits, such as decreased weight, reduced cost, and simplified manufacturing processes. As the amount of consumer generated solid waste continues to increase, the recyclability of plastics is also advantageous, as it is estimated that by volume, plastics may make up as much as one-quarter of all municipal solid waste. Therefore, the use of recycled plastics may assist in reducing the problem of municipal solid waste pollution. The use of plastics may also be beneficial in situations where a plastic material may be substituted for a material that is either non-renewable or of limited supply, such as timber. In addition, plastics are often resistant to moisture and insect damage, and may provide a substantially maintenance-free building material.
Because of these benefits, one of the more recent uses for plastic materials lies in the manufacture of plastic lumber products. Plastics, particularly high density polyethylene (HDPE) are being molded into increasingly popular products. For example, plastic lumber has recently become more widely used in the manufacture of picnic tables, park benches, patio furniture, and trash receptacles. However, because of the nature of its composition, plastic lumber made from HDPE, polyvinyl chloride (PVC), polypropylene (PP), or other polyolefins has thus far had insufficient stiffness and strength to allow its use in structural applications. This drawback may be even more pronounced when plastic lumber is manufactured from a wide variety of recycled mixed waste plastics rather than virgin resins.
The present invention addresses this deficiency by providing a plastic lumber product and method of manufacturing that may allow plastic lumber components to approach the stiffness and strength of natural wood lumber of similar dimensions. The present invention contemplates a composite product, whereby a plastic core is placed between one or more layers of a reinforced plastic laminate. For example, the plastic core may consist only of recycled HDPE or other polyolefins, may be a combination of HDPE commingled with other curbside collected plastics, or alternatively, may be made of virgin polyolefin resins.
It has been discovered that if a thin layer, or layers, of a reinforced plastic laminate is affixed to the plastic core, the stiffness and strength of the resulting plastic lumber component may be greatly increased. The reinforcing laminate may be attached to the plastic core via an adhesive, welding, or possibly by co-xtrusion. It has also been determined that an inner, tying interlayer can be placed between the plastic core and the reinforcing laminate to further promote adhesion therebetween.
The present invention discloses composite plastic lumber components that may be used safely in a wider range of high performance applications possibly replacing wood, especially where exposure to moisture, insects and rotting may be a problem. For example, when manufactured according to the method of the present invention, such composite plastic lumber components may be utilized for joists, beams, stringers or other structural functions, and may be especially useful in the construction of decks, boardwalks and bridges in marine and waterfront applications.